Typically, exterior coated film of a vehicle basically has structure of an electro-deposition layer, a primer layer, a base layer and a clear layer. Particularly, the primer layer is a coated film giving chipping resistance, however, a conventional primer coated film layer used in a vehicle body may have an inferior quality such as red rust phenomenon occurring by detachment of the coated film and excessive exposure of a base (e.g. iron sheet) after chipping, and therefore, customer satisfaction has dropped. Herein, the chipping resistance may mean a degree of damage caused by incoming small pieces of stones, a deicing salt, sand and the like during driving.
In the related arts, Japanese Patent Publication No. 3,097,989 discloses a polyurethane coating composition comprising a polyol-based reaction product, which contains low viscosity aliphatic or aromatic polyisocyanate having two or more isocyanate functional groups. However, the polyurethane coating composition may provide high elasticity and high tenacity to a coated film by using a mixture of hard urethane-modified polyol and soft urethane-modified polyol at all.
Further, U.S. Pat. No. 5,151,315 discloses a multi-layered composite material consisting of a middle layer including polycaprolactone and an outer layer including two polyurethanes. However, the multi-layered composite material may not include aromatic diisocyanate, and urethane polymers comprising a hard segment and a soft segment.
Thus, there is a need for a paint, which can prevent complete detachment of the coated film up to the electro-deposition layer even if the coated film is damaged by incoming stones, absorb most of impact at the primer layer, and minimize detachment of the coated film and red rust phenomenon after chipping at the same time.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.